As others have said, I did not dare get involved with this topic, because I
don't understand it well enough. I have spent the afternoon reading a new text
"Physics: A Contemporary Perspective" by Randall Knight from Cal. Poly at
San Luis Obispo, Addison Wesley. It is one of a new breed of textbooks
that are beginning to use the insights that the Physics Education Research
Community has brought to our attention. His discussion of the problem is
superb, and I now have new insights into this problem of zero work forces,
and where the enrgy goes when a block slides over the table. I think many
contributers to this list would anjoy it too.